tools,test: throw if common.PORT used in parallel tests

common.PORT should not be used in parallelized tests. (There can be a
port collision if another tests requests an arbitrary open port from the
operating system and ends up getting common.PORT before a test that uses
common.PORT uses the port.) In such a situation, throw an error.

PR-URL: https://github.com/nodejs/node/pull/17559


Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Gibson Fahnestock <gibfahn@gmail.com>